Auto-lamination machines or composite material placement machines (collectively “CMPM”) lay down individual or multiple strips of uncured pre-impregnated composite material by dispensing these strips out mechanically, and providing compaction pressure and heat to promote adherence against the tool or part surface. Examples of these technologies include automated fiber placement, automated tape laying, and filament winding. The use of compaction pressure and heat has increased with the desire to increase manufacturing productivity and laydown rates in high-speed CMPMs. Existing high-speed CMPMs and integrated heater systems can travel upwards of 2400 inches per minute during laydown.
The composite materials most often used in high-performance aerospace applications include a reinforcement and an epoxy based resin, which is typically sensitive to temperature exposure. There are presently two primary types of heater system technologies used with CMPMs, heated compressed air and infrared bulbs. Typically the infrared type heat source is configured to emit a wavelength of electromagnetic radiation that is absorbed by the resin to a relatively greater extent than the wavelength of electromagnetic radiation is absorbed by the reinforcement.
Both heater systems direct the heat towards the substrate or layup surface near or just ahead of the compaction point. This layup surface is often the previous layer or layers of composite material. Higher than desired temperature exposure to a previous layer or layers could result in premature cross-linking within the resin system, which could negatively effect mechanical properties of the composite material.
Various temperature measurement techniques have been attempted or are utilized. These include the use of non-contacting devices such as pyrometers and thermographic cameras, as well as the use of contact devices such as temperature sensitive films. Obstacles associated with the use of pyrometers and thermographic cameras include a sensitivity to reflected light and a dependency on the emissivity of the measured surface, and the need for line-of-sight. Infrared based heater systems often produce a bright reflection off the heated surface, resulting in artificially high temperature measurements when using pyrometers or thermographic cameras. Additionally, direct line-of-sight is typically not achievable due to machine geometry. Obstacles associated with temperature sensitive films include their inherent differences in emissivity, heat transfer properties, and lack of responsiveness.